EOL of ruby23 and default version of Ruby

[Takahiro Kambe <taca%NetBSD.org@localhost>]

Hi,

Support of Ruby 2.3 has ended on 31 Mar. 2019.  So, I'll retire ruby23
packages from pkgsrc.  (ruby22 is still remained only for
devel/ruby-redmine until someone update Redmine to newer release.)

And I'll plan to change default version of Ruby from current 2.4 to
2.5 since 2.5 has less compatibility problem and works fine in
general.

-- 
Takahiro Kambe <taca%NetBSD.org@localhost>